The invention relates to automatic welding apparatus for weld build-up, e.g. upon the inner wall of a tank or the wall surface of a large diameter bore, and on outer cylindrical and face surfaces as well.
In the past, it has been known to employ a welding apparatus using the MIG (metallic consumable electrode using inert gas) to deposit a layer of metal upon an outer cylindrical surface, e.g. of a shaft, or the inner cylindrical surface, e.g. of a bearing, for the purpose of making repairs to a surface that has damage or is out of required dimension due to wear and the like or is machined incorrectly, or for cladding a surface with a dissimilar material, e.g. a stainless steel cladding on the inside surface of a carbon steel bore. It has also been known to build-up outer cylindrical surfaces and face surfaces. Typically, after a layer of metal is applied over an area of the surface, the surface is returned to the desired diameter by a turning process.
In one type of prior art welding apparatus used for this process, the apparatus is stationary or fixed, making it necessary to transport the article to be repaired to the site of the welding apparatus, often resulting in considerable downtime. Also, in this type of prior art apparatus, the welding torch for applying the build-up layer is fixed, and it is necessary to mount the article to be repaired for rotation of the surface past the tip of the torch.
In many instances, the article to be repaired is located at the site too remote to permit it to be transported efficiently to the welding apparatus. Also, many types of articles are too large or bulky for mounting for rotation of the surface to be repaired past the welding torch tip.
In response to these needs, others have suggested a welding apparatus that may be transported to the site of the article to be repaired, with means for moving the welding torch tip along the surface upon which a build-up layer of metal is to be applied.
Automatic welding apparatus for effecting weld build-up about either an exterior surface or a bore surface are described, e.g., in U.S. Pat. Nos. 4,323,750; 4,215,809; 4,527,039; 4,550,235 and certain automatic welding machinery sold by Cecil Peck Company, of Cleveland, Ohio.
The apparatus described in U.S. Pat. No. 4,323,750 is specifically designed as a lining machine in which the workpiece rotates. It is made typically for large diameter pipe that is to be lined with another material as in lining a cylinder with stainless steel for corrosion resistance. In this machine, the whole welding apparatus enters the pipe which is then rotated on rollers.
The apparatus described in U.S. Pat. No. 4,215,809 is specifically designed for surface build-up, but the apparatus is a lathe and rotates the workpiece while the welding head remains stationary, thus requiring that the workpiece be of limited size and configuration. For example, it would be difficult to build up the inner diameter of a cross hole in the end of a long structure with this apparatus.
U.S. Pat. Nos. 4,527,039 and 4,550,235 by Fuwesi both describe portable apparatus for applying a weld bead to build up the inner surface of a bore on an article that may be stationary, and then using the major part of the same apparatus to turn the surface to achieve the desired diameter.
Regarding the apparatus of The Cecil Peck Company, generally, such welding apparatus consists of a module, equipped with all necessary mechanical and electrical components, that is adapted to be rotated about the parts to be welded. Typically, a standard commercially available MIG welding unit designed for linear welding is used in such apparatus. For radial adjustment, the entire unit, consisting of the wire feed adjustment, the wire feed motor, gear reduction assembly and the wire feed rolls, along with the torch head, gas hose, power cables and the wire reel, must be offset and rotated, necessitating abundant clearances. This entire unit must orbit the workpiece, even when welding a small bore. The welding power source and control box are the only components of the welding system that are remotely located from the weld site.
In addition to the above, U.S. Pat. No. 3,815,807 discloses a pipe welder made for joining two cylindrical objects, with no means for automatically stepping up to form contiguous beads for building up a surface. The machine is described as effecting only a 360.degree. weld. It is then reversed in order to disentangle power leads, gas hose and welding wire, and, therefore, it is difficult to use as a build-up machine.
Prior art welding apparatus having mechanisms for stepping-up the torch head after each circular weld has been finished typically include additional controls. These controls are provided for varying, e.g., the angular position of the torch head to the weld site or the radius of the circle that the nozzle will travel.
In a prior patent by one of the inventors here, Acheson U.S. Pat. No. 4,952,769, issued Aug. 28, 1990, the disclosure of which is incorporated herein by reference, there is described an automatic welding apparatus and method for achieving weld build-up, by which a torch is disposed for rotation within a bore for applying a uniform layer of metal for repair of the surface. According to that prior patent, the drive mechanism, the electrode wire supply feed and means for vertical adjustment of the torch tip are in fixed location outside of the bore, with the rotating torch tip extending therewithin. This arrangement permits the welding apparatus to be used for repair of relatively small diameter bores, e.g. down to 0.450 inch. The apparatus includes attachments for the torch that permit repair of bores of much greater diameter, e.g. up to 20 inches or more, with that prior art system. The weld bead is laid circumferentially, with the torch adjusted at the end of each rotation in a step-wise fashion in order to provide a more uniform layer built-up upon the surface.
Others have suggested welding apparatus for repair of relatively large diameter surface in which the welding wire and other of the mechanism are mounted for rotation with the torch. For example, McCollum U.S. Pat. No. 2,839,663 describes a welding apparatus for lining the bottom and/or sidewall of molten metal ladles, with the bead deposited in a spiral pattern. The wire feed is mounted on the rotating platform. A vertical rack-and-pinion arrangement is positioned to raise and lower the welding head relative to the platform. Smith U.S. Pat. No. 3,627,973 also describes a device for applying weld beads within a tank, with the welder reversed after each circumferential pass, the welding wire being fed from a fixed, external source.